Reaction and Diffusion Kinetics during Hydrothermal Carbonization by Means of SEM–EDX Analysis

Abstract

The reaction kinetics for carbonization of biogas slurry and the influence of diffusion for high-density feedstocks (pistachio shell) were investigated. The experiments were carried out with a 1.5 L batch reactor for hydrothermal carbonization at reaction temperatures of 190, 200, and 220 °C and a residence time of 0–160 min. The obtained hydrochar samples were dried and analyzed via scanning electron microscopy and a C, H, and O elemental analyzer. It was found that the average activation energy of the biogas slurry is 50.7 kJ/mol. In the case of the diffusion experiments, Thiele moduli of 1.21–1.61 were found, which indicates an influence on diffusion for the hydrothermal carbonization of pistachio shells.

Probing elemental speciation in hydrochar produced from hydrothermal liquefaction of anaerobic digestates using quantitative X-ray diffraction

“…3.2.3 Mineral functional groups. The mineral phase composition provided by XRD were conrmed by the 31 P, 25 Mg, and 43 Ca SS-NMR analysis with the same quantication technique as the 13 C SS-NMR to determine the functionalities distribution, i.e., spectral peak integration. The relative proportions of P, Mg, and Ca functional groups shown in Fig.…”

“…The DP-MAS SS-NMR of 13 C, 31 P, 43 Ca, and 25 Mg were performed using a 500 MHz Bruker Avance II NMR spectrometer, with a 4 mm triple resonance probe and operating frequencies of 200, 125, 34, and 55 MHz for 13 C, 31 P, 43 Ca, and 25 Mg, respectively. Protondecoupling techniques were employed to achieve high spectral resolution with high signal-to-noise ratio, narrower singlets, and less spectral overlap: (1) two-pulse phase-modulated proton-decoupling for 13 C, (2) continuous heteronuclear decoupling ( 31 P-1 H) on 1 H channel for 31 P, (3) spinal-64 1 H decoupling for 43 Ca, and (4) continuous-wave proton decoupling for 25 Mg. Detailed operating conditions including the 90°p ulse length, recycle delay, MAS rate, transient number, and reference compounds are given in Table S2 of the ESI.…”

“…The acquired 13 C, 31 P, 43 Ca, and 25 Mg SS-NMR spectra of hydrochar were divided into seven, four, ve, and three regions of chemical shi range, respectively, according to the functional group classication in the literature. 27,[55][56][57] Each region excluding the peaks of solvent and internal standard was integrated and normalized to the total spectral area using MNova 14.2.3 (Mestrelab Research) to obtain the relative region area percentages, which correspond to the functionalities distribution.…”

“…Similarly, the yield of inorganic nutrient in the hydrochar can be calculated based on the elemental content measurement using a colorimeter 20 or a spectrometry instrument, i.e., inductively coupled plasma with mass spectrometer (ICP-MS) or optical emission spectrometer (ICP-OES), 23 X-ray uorescence (XRF) spectrometer, 24 and energy-dispersive X-ray (EDX) spectrometer. 25 While the analytical techniques to measure the elemental composition are well-established, more efforts are required to improve the characterization of the elemental speciation. Spectroscopy techniques with Fourier transform infra-red (FTIR), X-ray photoelectron (XPS), and the 13 C, 1 H, and 31 P solid-state nuclear magnetic resonance (SS-NMR) are usually employed to observe the prole of chemical functionalities in the hydrochar.…”

“…The quantication follows the whole pattern tting (WPF) and Rietveld renement protocols for full diffraction pattern processing. 46,47 To validate the quantitative XRD results, (1) the elemental balances were calculated based on the measured mass yield and elemental content of all the product phases and (2) the distribution of chemical functionalities of hydrochar were measured using the direct polarization magic-angle spinning (DP-MAS) SS-NMR spectroscopy of 13 C, 31 P, 43 Ca, and 25 Mg. Subsequently, the liquid-state 13 C and 31 P NMR analysis of the biocrude and HTL-AP were performed to characterize the composition of the organic compounds and the distribution of phosphorus functional groups.…”